The present invention relates to an enlarged display panel having electroluminescent (EL) elements.
The electroluminescent display having fluorescent substance which emits light upon application of electric field is superior than a liquid crystal display in visibility and resolution. An organic fluorescent substance emits light with much lower voltage than an inorganic fluorescent substance such as zinc sulfide and calsium sulfide, so that the display may be driven by an ordinary integrated circuit.
Referring to FIG. 1, a conventional electroluminescent display panel has a glass substrate 1 on which a layer of indium-tin oxide (ITO) is deposited by chemical vapor deposition or vapor deposition to form a plurality of transparent electrode strips 2. On the transparent electrodes 2, a thick luminescent layer 4 of about severals tens of .mu.mm is disposed by screen printing, interposing a first insulating layer 3. The layer 4 may be a thin film formed by various deposition methods. A plurality of opposite electrode strips 6 are formed on the luminescent layer 4, interposing a second insulating layer 5 therebetween.
The opposite electrode 6 and the transparent electrodes 2 are disposed to extend in perpendicular directions to each other, thereby forming an X-Y dot matrix. In an active matrix display, either one of the X-ordinate and Y-ordinate serves as a scanning electrode array and the other serves as a data electrode array, each of which is driven by an IC.
When one of the transparent electrodes 2i and one of the opposite electrodes 6j are applied with a current, a pixel 4ij comprising the luminescent layer 4 at the coordinates (i,j) on the X-Y matrix is energized to illuminate it. Thus, an image is indicated on the display.
Various devices such as the IC are attached to the EL display panel to produce a display device. The product device undergoes various tests concerning exterior, displaying operation, reliability and mechanical strength of the panel. However, since each pixel has extremely delicate and complicated structure, a large portion of the matrix panel is proved to be defective by the tests. Thus, the yield of the production is small.
More particularly, supposing that one pixel per 10,000 pixels is defective, and the matrix panel comprises 280 by 120 pixels, the rate the defective matrix panel is manufactured is, EQU (280.times.120).times.(1.times.10,000)=0.33
Namely, one per three EL matrix panels is effective. The yield further decreases if the panel is provided with a thin film transistor (TFT) to impart a memory function thereto.
If the manufacturing process is strictly supervised for improving the yield, the cost of the EL panel inevitably increases. Moreover, a low yield makes it difficult to manufacture a larger EL display panel where a large number of pixels are used. Since the large EL panel requires various complicated examining processes, the manufacturing cost further rises.